Process of pasteurizing milk



Patented June 7, 1938 j, "UNITED? STATES rnocass or ms'ranmzmo MILK Rolan Jay Wightman, Little Falls. N. Y; assigno r' to Cherry-Barrel! Corporation,

Wilmington- Del., a corporation of. Delaware 1 No Drawing. Application April 1, 1936, Serial No. 72,111

4 Claims. (o1. 99-212) This 'invention relates 'to improvements in methods of pasteurization. While the improved methods of thisapplication are particularly desirable for pasteurizing milk and are .herein- 5 after described as so employed, the invention is not limited to the pasteurization of milk, but is also adapted for pasteurizing other substances,

such for example as cream, milk compounds, and vegetable and fruit juices.

and holding it at a prescribed temperature for a period of time, the length of which usually depends upon the pasteurizing temperature to which the milk is heated, and then cooling the milk to a 5, temperature suitable for bottling or storing it.

monly practiced, the raw milk has been heated to the required pasteurizingor holding tempera-.

'ture by a heating operation whichis uninterrupted by any cooling or lowering of the temperatureof the milk. Short time pasteurization, in addition to the saving of time it eifects, is considered advantageous over long time processes because the milk is in contact with the equipment for a much shorter time, with the result, that the milk has less chance for picking up metallic or o flavors. Experience with short time pasteurization processes indicates that the flavor of the milk is improved bythe short time methods, it being believed that the enzymes have not'been 40 affected, and that the final pasteurized product' has more nearly the flavor of fresh, sweet, raw milk.

Not infrequently, however, short time milk paste'urizingmethods, as practiced at present, are

unsatisfactory on account of obiectionably high bacterialvcountsin the pasteurized milk. The

longtime and short .tim'eholding syster'nsJf both are operated properly, show very little diiference in cream layer or volume. Normally there should be very little difference shown in bacterial reduction, especially in bacteria of pathogenic type, although it'has been noticed that a heat-resisting type of bacteria has been more prevalent in the short time systems thaninthelong time The objects of my invention are to provide a Milk is commonly pasteurized by heating it to novel process ofipasteurizatmn giving improved results over previous processes; also to improve short time pasteurization methods so as to materially reduce the bacterial counts in the-pasteurized products; also to iniprove shorttime milk 5 pasteurizing'methods in a way that will not impair the cream layer or volume or the flavor of the milk; also to provide an expeditious and efilcient method of pasteurizing milk which will improve the cream layer and give a lower bacterial count than previous short time pasteurization methods; I and also to provide a -method of pasteurizing milk which willinsure satisfactory results as to bacterial reduction, cream layer and flavor in th pasteurized milk. According to my improved pasteurization methods, the milk, as heretofore, is heated to and held at a suitable temperature for the appropriate period of time, but prior or preliminarily. to this heating and holding treatment the mi1k is sub- 20 jected to shock or relatively sudden changes in temperature one or more times, after which said heating and holding treatment is carried out. For example, the milk may be first heated from a cold condition to a predetermined temperature 25 not lower than about 150 F. and not above about 160 F. (said heated temperature being preferably from 155 to 158 F. inclusive), and then cooled down to a temperature of about 145 F. or less, following which preliminaryheatingand cooling .the milk is again heated to a temperature of such that its action inconjunction with the final heating and holding does not impair the cream layeror volume or the flavor of the milk 45 any more than is done in ordinary short time pas- I ,teuiization. On the "c nt 'ary;'improvements in the cream layerfas wellasfgreatly reduced bacterial counts have been obtained in pasteurizlng milk by the hereindescribed methods.

In the preliminary heating of the raw milk, if its temperature is much below. F., it is heated up to about 100 F. and may be then raised from that point to'the before mentioned predetermined temperature between and 100 .degrees F. m a period of time which may vary periodmayvaryinlengthiromaboutoneseeond 'Thecoolingoi'themilkdowniromsaidpre-.

liminary high temperature to approximately 145 or less may be eiiected in a period of time varying from about one second to one minute more or less, and the time for again heating the milk to the final minimum temperature of about 160" at which it is held for the'minimum period of about fifteen seconch, may be from about two seconds to two minutes more or less, depending upon the. particular type oi. equipment used and the length of time required for the milk to flow over or I through it. The time for the final cooling of the milk to bottling or storing temperature may vary over. a considerable range. such as from about two seconds to four minutes more or less.

Good results have been obtained in practice by carrying out the method with the following temperature and time schedule:

The raw milk at a temperature of approximately 40 1''. is raised to around F. in approximately two minutes and further heatedtrom that point to 158 I". as near as possible in about one minute, then promptly cooled down to F. in approximately one minute, then heated from this temperature to approximately 160 F. in about one and one-half minutes and held at that temperature for approximately fifteen seconds, and finally cooled to' about 38 F. in about three seconds. This procedure reduced the bacterial count more thanthirty-five percent over previous ordinary short time pasteurization with the same apparatus and the cream layer was also improved.

Ii'desired-Jherecanbeashortholdingperiod between the preheating and precooling stages. Thatis, themilkmaybeheld atits preheated temperature around to 158 for ashort time toabouttensecondaandshouldbeadjmtedaccording to. the preheated temperature med. Whilesuchprelioldingperiodisdeairableinperiormin'gmymethodwithsometypesoi'pasteurixingapparamaintheuse oi'othertypesofapparatmitisdeairablenottohaveanyholding periodm betweenthepreheaflngandpreoooling Promthedescriptionoithemethod, itwill'benotedthatinthefirstorpreliminary hell-inl.themilkisheatedfromappmximately 100F.toapredeterminedtemperature.andin itisheatedtoapredeter-.

minedte'mperatureandboth-ottbmeteinperatmacanbefixedandcontrolledbymitableautomatiemeanaknownintheart.

Inthemethodsasahovedescribeithemilkls, preliminarilyheated and cooled only once. but

whenbacterimwhicharehardtokIILarepruentinthemiILorwhenevenmrther reduction of baeteriaiis desired. muiflple preliminaryheatingandcoolingtreaianentsbeiore the final heatingandholding process, maybe employed. Ibrex'ample,therawmiikatamd 40I'.ma.ybe'heatednpto155'to158'1 '.insay tromtwosecondstotwo minutes moreorlel.

thencooied down to 145 1". or lessin tromtw'o secondstotwominutesmoreorless,andthenreheated to 155to 158' and recooled to 145 or lcssinaboutthesameperiodsoi' timeasusedior temperature oi the milk to about 100 F. and

preliminarily heating the milk from that temperature to a temperature oi approximately 100 1".inaperiodoitimenotexceedingtourminutes.

then promptly cooling the milk bei'ore pasteurization thereof occurs at least to approximately 145 F. in a period oi! time not exceeding about one minute, then heating the milk to a temperature of approximately 160 F. in a period 0! time not exceeding about two minutes and holding it approximately at 160 1''. for approximately filteen seconds, and then cooling the milk.

2. The hereindescribed short time method of pasteurizing milk which comprises preliminarily heating the milk to a temperature between 155 F. and 160 R, such portion of said heating which raises the temperature oi'the milk over and above 100 1". being accomplished ina period of time not exceeding four minutes, then cooling the milk at least to approximately 145 1'. within a period of time not exceeding one and one-half minutes from the time the milk attained said preliminary heated temperature, then heating the milk to a final high temperature or about. 100 F. in a period of time not exceeding about two minutes, and holding it approximately at said a last mentioned temperature for a period of time 

